diff --git a/bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/cleanupaddon/CleanupAddon.java b/bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/cleanupaddon/CleanupAddon.java
index c2fab02e0657..beb4e0f9dfee 100644
--- a/bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/cleanupaddon/CleanupAddon.java
+++ b/bundles/org.eclipse.e4.ui.workbench.addons.swt/src/org/eclipse/e4/ui/workbench/addons/cleanupaddon/CleanupAddon.java
@@ -346,16 +346,13 @@ private void subscribeRenderingChanged(
 				int visCount = modelService.countRenderableChildren(container);
 
 				// Remove stacks with no visible children from the display (but not the
-				// model)
-				final MElementContainer<MUIElement> theContainer = container;
-				if (visCount == 0) {
-					Display.getCurrent().asyncExec(() -> {
-						int visCount1 = modelService.countRenderableChildren(theContainer);
-						if (!isLastEditorStack(theContainer) && visCount1 == 0) {
-							theContainer.setToBeRendered(false);
-							transferPrimaryDataStackIfRemoved(theContainer);
-						}
-					});
+				// model). Since event delivery is synchronous (EventBroker.send via
+				// EventAdmin.sendEvent and Display.syncExec), the visCount reflects
+				// the actual state at the time of this event and can be acted upon
+				// immediately without deferring via asyncExec.
+				if (visCount == 0 && !isLastEditorStack(container)) {
+					container.setToBeRendered(false);
+					transferPrimaryDataStackIfRemoved(container);
 				} else if (container.getParent() != null) { // omit detached windows
 					// if there are rendered elements but none are 'visible' we should
 					// make the container invisible as well
diff --git a/tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java b/tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
index b62b0d41d6ac..d646a2150eef 100644
--- a/tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
+++ b/tests/org.eclipse.e4.ui.tests/src/org/eclipse/e4/ui/tests/workbench/PartRenderingEngineTests.java
@@ -64,7 +64,6 @@
 import org.eclipse.swt.widgets.Shell;
 import org.eclipse.swt.widgets.ToolBar;
 import org.eclipse.swt.widgets.Widget;
-import org.eclipse.ui.tests.harness.util.DisplayHelper;
 import org.junit.jupiter.api.AfterEach;
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Disabled;
@@ -2447,12 +2446,9 @@ public void ensureCleanUpAddonCleansUp() {
 		assertTrue(partStackForPartBPartC.isToBeRendered(), " PartStack with children should be rendered");
 		partService.hidePart(partB);
 		partService.hidePart(partC);
-		// DisplayHelper.waitForCondition() handles event processing via Display.sleep()
-		// and retries. Calling spinEventLoop() here creates a race condition where
-		// events may be processed before CleanupAddon's asyncExec() is queued (line 352).
-		assertTrue(
-				DisplayHelper.waitForCondition(Display.getDefault(), 30_000,
-						() -> !partStackForPartBPartC.isToBeRendered()), "CleanupAddon should ensure that partStack is not rendered anymore, as all childs have been removed");
+		contextRule.spinEventLoop();
+		assertFalse(partStackForPartBPartC.isToBeRendered(),
+				"CleanupAddon should ensure that partStack is not rendered anymore, as all childs have been removed");
 		// PartStack with IPresentationEngine.NO_AUTO_COLLAPSE should not be removed
 		// even if children are removed
 		partService.hidePart(editor, true);